The present invention relates to electrically operated scales, and in particular to scales of the type wherein a variable-capacitance load cell is used to determine the weight on the scale.
In prior art constructions of smaller weighing devices, a yoke-like structural mechanism is provided to support the scale platform and to transfer the weight of the platform into a single load cell. The capacitance of this cell is then measured by a measurement circuit to provide an indication of the total load on the platform.
In the construction of larger scales, such as truck scales, it is known to support a platform by several, e.g., three or four, independent load sensor units and to separately measure the load on each sensor and sum the individual loads to determine the cumulative weight on the platform. In smaller scales, however, such as those which have a maximum load range under several kilograms or those intended to have an accuracy of several milligrams, this multiple-sensor construction is not generally employed. Rather, the aforementioned yoke-type or related beam or balance-type structures are used to convey the weight to a single sensor. Such intermediate mechanical structures are relatively costly, and may introduce frictionally-caused measurement errors and mechanical wear effects.
While the mounting yoke could be eliminated and simply replaced by a four-point platform mounting on four separate load cells, this entails providing four capacitance measuring circuits in order to determine the load at each cell at one point in time. To provide multiple sets of sensing circuitry as well as multiple load cells, however, would offset the savings achieved by elimination of the mechanical suspension structure.